Circuits for unimoding crossed field devices



Feb. 1s, 1964 M. R. BOYD 3,121,822

CIRCUITS FOR UNIMODING CROSSED FIELD DEVICES Filed-Oct. 28, 1960 United States Patent Ofiice lZl/Z Patented Feb. 18, 1954 3,12LSZ2 CRCUTS FOR UNEMODHNG GROSSER MELD DEVECES Malcolm R. Boyd, Schenectady, NKY., assigner to General Electric Company, a corporation of New York Filed Oct. 2t?, weil, Ser. No. 65,717 1G Claims. Cl. SiS-39.69)

This invention relates to an electron discharge apparatus of the type commonly called a magnetron, for producing electromagnetic waves of high frequency.

Magnetron oscillators are well known and generally include a cathode centrally disposed in a hollow anode which has a plurality of anode segments or vanes protruding radially inwardly toward the cathode. The spaces between pole faces are resonant slots or resonant cavities. The anode is made electrically positive with respect to the cathode to attract electrons emitted by the cathode and a constant magnetic field perpendicular to the electric field so produced and substantially parallel to the cathode, is established to further influence the trajectories of electrons emitted from the cathode. Under proper conditions of electric and magnetic fieldl intensity, electron iow in the space between the cathode and anode sections establishes a high frequency alternating potentiais or oscillations at the inner anode sections. The potentials at adjacent anode sections at any instant of time may be in exact phase opposition or in other words, 180 out of phase with each other, in which case the magnetron is said to be operating at pi mode, or the potentials at adjacent pole faces may be less than 180 out of phase with each other wherein the magnetron is said to be operating at a mode other than pi mode.

it is an inherent characteristic of magnetrons that operation thereof in different modes entails oscillation at different frequencies. Tiat is, operation of any specific magnetron in any particular mode produces a particular frequency and the frequencies of oscillation of that magnetron in dierent modes are also different. vIt frequently occurs that in magnetron oscillators without special provisions for establishing a contrary characteristic, the frequencies of operation in adjacent modes are narrowly spaced and the magnetron is readily susceptible to shifts in operation between adjacent modes. This is particularly true when the magnetron is loaded at a frequency of a specific mode wherein the magnetron shifts to operation at another mode and therefore, at another frequency that is not so heavily loaded.

The satisfactory operation of electronic apparatus often depends upon an accurate, and stable source of high frequency electromagnetic ener-gy. Accordingly, the mode shifting ch racteristic of magnetrons as hereinabove described renders the same objectionable in situations requiring such a source of relatively precise and stable electromagnetic energy.

It is known to lessen the tendency for mode shifting in magnetrons from pi mode by the-provision of strapping wherein a pair of spaced, adjacent conductive straps are each connected to different alternate anode sections or vanes. With this arrangement, each strap connects poles of like polarity and as a consequence the potentials of the straps are 180 out of phase with each other. Because of the symmetry and phasing of alternate poles, no current flows in the straps at the frequency of pi mode. Thus, the capacity between the straps is added to the capacity between anode sections or in other words, to the capacity of the resonant cavities. The result of such added capacity is to lower somewhat, the frequency of operation of the magnetron in the pi mode. Simultaneously, since the phase shift between anode sections at modes other than pi mode is other than 180, potential difference across these sections occur for these other strapping arrangement is to modes and currents at frequencies of these other modes will flow in the straps to introduce an effective inductance in parallel with the inductance of the cavities, raising the frequency of oscillation at adjacent modes. Thus, the difference in operating frequencies between adjacent modes is increased and the shift in operation from one mode to the other is rendered less .likely and stability of operation is increased.

It is noted, however, that the aforedescribed technique of improving the operational stability of a magnetron is not completely effective and that in many circumstances, in magnetrons strapped vaccording to known practice, a shift in mode and frequency of operation results from vloading thereof.

yIt is, accordingly, a primary object of my invention to improve the operational stability of strapped magnetron oscillators.

It is another object of my invention to facilitate operation of a magnetron oscillator in a predetermined mode and suppressing any tendency to operate in any other mode.

Pursuant to the foregoing objects and in accordance with afeature of my invention, operation of a magnetron at pi inode may be established and maintained notwithstandingheavy loading or other influences on the magnetron, by -the provision of two pairs of continuous ring straps, each ybeing short circuited to the other of the pair over a fraction of its length and each-being connected to a different, every fourth Vane or section of the anode. The short circuiting between straps may be continuous or discontinuous about the circumference thereof. Under these circumstances, the portion of the magnetronhaving the shorted straps `has conductive connections between vanes and operates as a conventionally strapped magnetron for mode stabilization and along the unshorted portions, a capacitive coupling exists between Vanes which are desired to be operatedin phase. The effect of these different strapping arrangements is to produce two different frequency versus.phase-shift-prev-vane characteristics the curves of which are convex to each other and which are coincident at a single point at pi mode. The frequency separation between curves dider increasingly at modes away from pi mode. The effect of the capacitive increase the slope of one curve over that which would be obtained with an unstrapped arrangement and, therefore, to enhance the separation of frequency of operation between different portions of the magnetron at modes removed from pi mode.

ln copending Donald A. Wilbur application Serial No. 65,716, filed October 28, 1960, .entitled Mixed Lines Crossed Fields Oscillator or Amplifier and assigned to the assignee of the present application, there is disclosed and broadly claimed apparatus embodying a slow wave structure having two or more portions with frequency versus phase shift per section characteristics which intersect for only one frequency. The invention of the said Wilbur application was made prior to my invention and is to be regarded as prior art with respect to the invention of this application.

Other and further objects and advantages will appear by referring to the following detailed description of the invention considered with the accompanying drawings in which:

FIGURE 1 is a cross-sectional elevation of a magnetron oscillator according to the invention,

FIGURE 2 is a graph representing the characteristics of conventionally strapped and capacit-ively strapped magnetrons,

FIGURE 3 is a partial plan view taken along section 3 3 in FIGURE 1 showing the connections between straps and vanes of the magnetron, and

FIGURES 4, 5, 6 and 7 are partial, elevational views taken along sections 4 4, 5 5, 6-6 and 7-7, respectively, in FIGURE 3 showing the respective connections between straps and vanes in the magnetron oscil-lator.

Referring now to the drawings, 10 represents generally an entire magnetron structure embodying my invention and includes an anode represented generally at 12 and a cathode represented generally at 14. As shown more clearly in FIGURE 3, the anode includes a ring 16 being interiorly notched to receive the respective ends of a plurality of vanes 18A through 18L and the ring 16 is maintained in position by an outer housing 20 which along a portion 22 of its length encloses the anode and extends axially therefrom along portions 24 and 26 joined by tapered portion 28, An end closure member is joined at its outer periphery to housing 20` about the free edge of portion 22. For abstracting energy from the magnetron, a spider having a plurality of arms 31 each of which is connected to one of the vanes through leads as shown at 32 is connected to an inner conductor 33 of a coaxial output line having an outer conductor 34.

For establishing an interaction region, the inner ends of the vanes terminate along a circumference of a circle and the sectorial portions between pairs of vanes comprise cavities resonant at a `frequency of the order of the desired operating frequency of the magnetron. Cathode 14 is disposed within the region formed by the vane tips, and includes a hollow cylindrical emitting surface having planar ends 42 and 44 secured to a conductive cup 46 shown inverted in FIGURE l. A pair of circular brackets 4S and 50 are secured to respective ends of cup 46 and engage the inner surfaces of ends 42 and 44 to mount the cathode 40. Aligned notches in the brackets accommodate a plurality of ceramic columns 52 about the cup 46 for facilitating the mounting of a heater wire 54 which is spirally wound about the ceramic columns collectively. Heat may be produced by wire 54 by an electric current passed through the same and such heat raises the temperature of cathode 14 to a point of electron emissivity. To intercept stray electrons emitted from cathode 14, a pair of end hats 56 and 58 are mounted at the ends of cup 46 and extended therefrom to the radius of cathode 14.

For mounting and supplying electrical connections to cathode 14 a mounting post represented generally at 60, is provided which includes a nested arrangement of several components bonded or secured together in a suitable manner. A hollow conductive member 62 is conductively coupled with the cathode through a metal ring 64 which is interposed between and secured to the mem ber 62 and bracket 50 and a ange 66 near the end of member 62 provides an abutment support for a frustoconical insulator 68. A sleeve 70 with an inwardly directed ange 72 is in abutment and attachment with the other end of insulator 68 and this sleeve may be secured to axial portion 26 of housing 20. Connections to heater wire 54 are facilitated through leads from ends of wire 54 extending through the Wall of cup 46 and being insulated therefrom at 71 and 73, to generally annular terminal members 74 and 76 separated from other parts and each other by annular insulators 7S and 80. Electrical connections to cathode 40 are made through a line 7S connected to a conductive tube 77 serving as a terminal member. Each of the terminal members is connected exteriorly to lines leading to other circuitry. A tubulation 79 for evacuation purposes is provided as the lowermost portion of post and communicates with the interior of the magnetron through the hollow of post 60.

The interaction region of the magnetron is immersed in a magnetic field produced by a pair of electromagnets having respective pole pieces 81 and 82 and respective coils 83 and 84 energizable by a direct current of substantially constant value.

In accordance with an important -feature of my invention a first pair of conductive straps 86 and 88 and a second pair of conductive straps 90 and 92, each strap being circular-ly continuous, are mounted at one side of the Imagnetron vanes for contact with selected vanes and similar pairs of straps 86' and 88 and 9G and 92 are mounted at the other side of the vanes also for contact with selected vanes. Each strap is conductively connected to every fourth vane and each vane is connected to only one strap. Thus, in a twelve vane magnetron as shown in FiGURE 3 each strap is connected to three vanes symmetrically spaced about the circumference of the anode. In the specific embodiment shown, strap is connected to vanes 18A, 18E and 181, strap 88 is connected to vanes 18C, 18G and 18K and strap 90 is connected to vanes 18B, 18E and 131 and strap 92 is connected to vanes 18D, 15H and 13L. The vanes are also connected to different straps of the four at the other side of the vanes. Vanes 18A, 18E and 181 are connected to strap 92', vanes 18B, 18F and 18] are connected to strap 88', vanes 18C, ISG and 18K are connected to strap 90 and vanes 18D, 18H and SL are connected to strap 86. As illustrated in representative detail FIGURES 4, 5, 6 and 7, each vane such as vanes 18B, 18C, 18D and 18E are connected to a strap of a pair disposed at diierent radii at different sides of the vane to effect a balance in the structure.

Further, in accordance with this feature of my invention, the pairs of straps S6 and 88 are connected together over a portion or portions of their lengths less than the total length and each of the other pairs of straps and 92, 86 and 88 and 9G and 92 are also connected together over a portion or portions of their lengths as shown with respect to 86 and 88 and 90 and 92 in FIG- URE 3. Thus, conductive members 93 and 94 interconnect segments of pairs of straps 86 and 88 and 90 and 92. Similarly, conductive members 9S and 96 interconnect corresponding portions of pairs of straps 86 and 88 and 90 and 92.

The particular extent of interconnection of pairs of straps or the particular location or locations of interconnections may be varied over wide limits, it being essential only to leave a portion thereof not interconnected so as to impose a discontinuity to unwanted modes tending to propagate in the magnetron. With this construction, along the short circuited portions of the straps the magnetron appears and operates as a conventionally, conductively strapped magnetron for pi mode operation while along non-short circuited portions it appears as a capacitively strapped magnetron. Thus, for example, pairs of straps may be interconnected continuously over one-half of their lengths and be disconnected over the remaining one-half of their lengths whereby the magnetron appears as a conventionally, conductively strapped structure over one half of its circumference and as a capacitively strapped structure over the other one-half. As further examples, the straps of each pair may be interconnected intermittently over several portions of their lengths, it being necessary only to provide an unconnected or connected portion long enough to render the magnetron a conventionally, conductively strapped or capacitively strapped structure over such lengths rather than merely present a slight disturbance. As a still further example, the pairs of straps may be short-circuited over different arcuate portions and over different circumferential lengths.

.The effect of the discontinuous interconnection of straps may be better understood by reference to FIGURE 2 of the drawing wherein curves 97 and 98 represent frcquency variation of magnetron 10 versus the phase difference per section between adjacent vanes for the capacitively strapped and conventionally, conductively strapped arrangements, respectively. With respect to curve 97 for a capacitively strapped structure, it is observed that at pi mode wherein the phase shift between vanes is pi radians or operation is at a point a on the curve where the frequency is represented by f1 and that for the same magnetron with conventional strapping, according to curve 98, operation at pi mode results in the operation at the same frequency f1 and the same .point a. In other words, point a is common to curves 97 and 98 and operation of a magnetron at pi mode either capacitively strapped or conventionally, conductively strapped results in the same operating frequency. Thus, when it is desired to operate at pi mode, it is immaterial whether the pairs of straps are conductively connected or capacitively connected.

For operation of the magnetron at a mode other than pi mode, however, as represented at mode m in FIG- URE 2, for example, for a capacitively strapped magnetron anode portion, operation is at point b and thus, at frequency f2 and for a conductively strapped magnetron anode portion operation is at point"c and thus, at frequency f3. It is readily observed that the frequency separation between points c and b is considerable. The relatively large slope of the sides of curve 97 results from the capacitive strapping7 of a portion of the anode. Accordingly, the magnetron to operate at mode m would be required to repeatedly shift between these frequencies of operation which it is not so inclined to do. That is, with the respective pairs of straps intermittently short circuited, the magnetron appears intermittently as a conductively strapped and as a capacitively strapped structure at modes other than pi mode. Thus, propagation of modes other than pi mode would entail the continuous shift between vwidely spaced frequencies. Since these frequencies are rather widely separated, the magnetron is strongly influenced to operate only at the pi mode.

While the present invention has been described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. An apparatus for producing high frequency electromagnetic oscillations comprising a plurality of symmetrically positioned, convergent, conductive vanes, a cathode equidistantly -spaced from each of said vanes and means producing a magnetic iield in the region between said vanes and cathode and perpendicular to a line between said cathode and any of said vanes, means applying a potential to lsaid vanes positive with respect to said cathode, means for conductively connecting each of said vanes to the fourth vane therefrom and means intermittently conductively connecting said conductively connecting means together over a substantial length thereof whereby propagation of modes other than pi mode in said apparatus is minimized.

2. A magnetron comprising a plurality of vanes symmetrically positioned with respect to each other, a cathode spaced from each of said vanes and means for applying a potential to said vanes positive with respect to said cathode, means for establishing a magnetic field in the region between said vanes and said cathode and being perpendicular to a line between any one of said vanes and said cathode, two pairs of straps, each strap being connected to a different every fourth Vane of said plurality and means intermittentiy conductively connecting the straps of each of said pairs together over a substantial length thereof, whereby propagation of modes other than pi mode in said magnetron is minimized.

3. A magnetron apparatus for producing high frequency electromagnetic oscillations comprising a plurality of symmetrically positioned convergent, conductive vane-s, a cathode equidistantly spaced from each of said vanes and means establishing a magnetic field within the region of said vanes and cathode and being perpendicular to a line between said cathode and any one of said vanes, means applying a potential to said vanes positive with respect to said cathode, two adjacent pairs of straps, each vane being conductively connected to only one strap of said adjacent pairs of straps, means for connecting each strap to the other strap of said pair over a length less than the entire length of the strap whereby oscillations at modes other than pi mode are minimized in said magnetron.

4. A magnetron apparatus for producing high frequency electromagnetic oscillations comprising a plurality of symmetrically positioned, convergent, conductive vanes, a cathode equidistantly spaced from each of Said vanes and means producing a magnetic eld between the region of said vanes and cathode and being perpendicular to a line between said cathode and any one of said vanes, means applying a potential to said vanes positive with respect to said cathode, two pairs of straps, each of said raps being connected to sets of dilferent vanes with each set including every fourth vane of said plurality of vanes and means conductively connecting each strap to the other Strap of that pair of straps over a fraction of its length.

5. A magnetron apparatus for producing high frequency electromagnetic oscillations comprising a plurality of symmetrically positioned, convergent, conductive vanes, a cathode centrally disposed with respect to said vanes and being spaced therefrom, means producing a magnetic ield in the region between said vanes and cathode and being perpendicular to a line between said cathode and any one of said vanes, means applying a potential to said vanes positive with respect to said cathode, two pairs of straps each of said straps being conductively connected to sets of different vanes with each set including every fourth vane of said plurality and each vane being connected to only a single strap, means establishing a continuous portion of conductive interconnection between the straps of each pair, whereby propagation of modes other than pi mode in said magnetron is minimized.

6. An apparatus for producing high frequency electromagnetic osciliations comprising a plurality of symmetrically positioned, convergent, conductive vanes, a cathode centrally disposed with respect to said vanes and being spaced from each of said vanes and means producing a magnetic ield in the region between said vanes and cathode and being perpendicular to a line between said cathode and any of said vanes, means applying a potential to said vanes positive with respect to said cathode, two pairs of straps, each of said straps being conductively connected to every fourth vane of said plurality and each vane being connected to only a single strap, means establishing conductive interconnection between the straps of each of said pairs over a plurality of spaced portions of said straps whereby propagation of electromagnetic modes other than pi mode in said magnetron is minimized.

7. An apparatus for producing high frequency electromagnetic oscillations comprising a plurality of symmetrically poistioned, convergent, conductive vanes, a cathode centrally disposed with respect to said vanes and being spaced from each of said vanes and means pr0- ducing a magnetic field in the region between said vanes and cathode and being perpendicular to a line between said cathode and any of said vanes, means applying a potential to said vanes positive with respect to said cathode, two pairs of straps on one side of said vanes, each of said straps being conductively connected to every fourth vane of said plurality and each vane being connected to only a single strap of said further pairs, means establishing an interconnection between the straps of each of said pairs over a plurality of spaced portions of said straps whereby propagation of electromagnetic modes other than pi mode in said magnetron is minimized.

8. A magnetron apparatus for producing high electromagnetic oscillation comprising a plurality of symmagnetic oscillations comprising a plurality of symcathode equidistantly spaced from each of said vanes and means producing a magnetic field between the region of said vanes and cathode and being perpendicular to a line between said cathode and any one of said varies, means applying a potential to said vanes positive with respect to said cathode, two pairs of straps, that of said straps being connected to every fourth vane of said plurality and each strap being connected to different varies than the other of said straps and means connecting each oi said straps to the other strap of each pair over a fraction of its length and each short circuiting connection being over a different arcuate portion of said straps.

9. An apparatus for producing high frequency electromagnetic oscillations comprising a plurality of symmetrically positioned, convergent, conductive vanes, a cathode equidistantly spaced from each of said varies and means producing a magnetic lield in the region between said vanes and said cathode, said field being perpendicular to a line between said cathode and any of said vanes, means applying a potential to said vanes positive with respect to said cathode, means conductively interconnecting all alternate varies along a fraction of the circumference of said apparatus and means providing a capacitive coupling between all alternate vanes along another fraction of the circumference of said apparatus.

10. Magnetron apparatus for producing high fre quency electromagnetic oscillations comprising an anode structure including a plurality of crcumferentially spaced conducting portions extending radially inwardly and dctining a generally circular array of high frequency circuits, said conducting portions terminating short of the center to provide an opening and means for supplying electrons in proximity to the ends of said conducting pori tions including means defining an annular space charge region in said opening and subjecting the electrons therein to mutually perpendicular electric and magnetic fields and a conductive structure for strapping said radially extending portions including means conductively connecting all alternate portions together near the inner ends thereof over a portion of said anode structure defining several adjacent circuits and conductively connecting every fourth anode portion over a second portion of said anode defining several circuits and capacitively coupling together the alternate anode sections of said second portion.

References Cited in the le of this patent UNITED STATES PATENTS Posthumus s Oct. 18, 1955 

3. A MAGNETRON APPARATUS FOR PRODUCING HIGH FREQUENCY ELECTROMAGNETIC OSCILLATIONS COMPRISING A PLURALITY OF SYMMETRICALLY POSITIONED CONVERGENT, CONDUCTIVE VANES, A CATHODE EQUIDISTANTLY SPACED FROM EACH OF SAID VANES AND MEANS ESTABLISHING A MAGNETIC FIELD WITHIN THE REGION OF SAID VANES AND CATHODE AND BEING PERPENDICULAR TO A LINE BETWEEN SAID CATHODE AND ANY ONE OF SAID VANES, MEANS APPLYING A POTENTIAL TO SAID VANES POSITIVE WITH 